Bolus tracking x-ray positioner

ABSTRACT

An x-ray positioner is provided having two independently articulated arms supporting an x-ray tube and x-ray detector, respectively, that are mounted offset to the patient and controlled to track a bolus travelling through a patient. A controller is provided with feedback information regarding the bolus to determine the rate of travel, and to produce motion signals to the arms to automatically track the movement of the bolus.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to U.S. Provisional Patent Application Serial No. 60/334,745 and entitled “X-RAY POSITIONER WITH SIDE-MOUNTED, INDEPENDENTLY ARTICULATED ARMS” filed on Nov. 15, 2001, the disclosure of which is hereby incorporated by reference as if set forth in its entirety herein.

BACKGROUND OF INVENTION

[0002] This application relates to medical x-ray positioners and in particular to a positioner using independently articulated arms to support the x-ray source and x-ray detector particularly suited for tracking a contrast bolus moving within a patient.

[0003] Conventional x-ray positioners provide mechanical supports to hold an x-ray source and x-ray detector in opposition about a patient for a limited number of specific procedures. For procedures in which the patient is standing, the x-ray source may be attached to a pillar allowing adjustment in its height as directed toward an x-ray detector attached to an opposing wall or a second similar pillar. For procedures in which the patient is supine, the x-ray source and detector may be attached to opposite sides of a patient table. Alternatively the x-ray source and the detector may be attached to opposite ends of a C-arm which is supported by a sliding collar allowing the angle of the x-rays through the patient to be varied.

[0004] Multi-axis robotic arms, positioned above and below the patient table, have been proposed to provide support for the x-ray source and x-ray detector such as may reduce interference between the support structure and other equipment and personnel. See, for example, U.S. Pat. No. 6,200,024 to Negrelli citing U.S. Pat. No. 4,894,855 to Kresse.

[0005] Such systems require complex multi-axis movement for simple adjustments of the x-ray tube and detector in angulation or translation, and appear to have limited utility for certain common x-ray procedures such as those requiring the patient to stand. Further such systems make it difficult or impossible to swap the location of the x-ray source from beneath the patient to above the patient, when the patient is supine, and an improved image might thereby be obtained. The limited axes of freedom provided by conventional positioners limit their ability to automatically track a bolus travelling through a patient's body.

SUMMARY OF INVENTION

[0006] The present invention provides an x-ray positioner having increased axes of freedom compared to conventional systems to enable the positioner to automatically track the movement of a bolus through a patient.. Generally the invention provides a bolus tracking x-ray positioner having an x-ray source producing an x-ray beam directed along a source axis, and an x-ray detector detecting x-rays received along a detector axis. A first and second articulated arm holds respectively the x-ray source and the x-ray detector in opposition about a patient volume for movement along a bolus path. An axis controller operates according to a stored program to: (i) recieve image signals from the x-ray detector, (ii) process the image signals to identify movement of a bolus of contrast medium within a patient, and (iii) send movement signals to the first and second articulated arms to move the x-ray source and x-ray detector to follow the bolus with movement of the bolus through the patient.

BRIEF DESCRIPTION OF DRAWINGS

[0007]FIG. 1 is a perspective view of one embodiment of the positioner of the present invention showing offset mounting of two independently articulated arms holding an x-ray source and x-ray detector assembly, respectively;

[0008]FIG. 2 is a perspective view of the detector of FIG. 1 showing a tilting upward of an integral display of the detector assembly and axes of movement of a control handle supported by the detector assembly;

[0009]FIG. 3 is a cross-sectional view of the detector assembly of FIG. 2 taken along lines 3-3 of FIG. 2 showing the normal registration of an x-ray detector and the display;

[0010]FIG. 4 is a view (top or side) of the articulated arms of the FIG. 1 showing, in phantom, arm movement implementing an increased source-to-detector distance;

[0011]FIG. 5 is a side elevational viewing of the articulated arms of FIG. 1 showing positioning of the arms for lateral imaging;

[0012]FIG. 6 is an exploded perspective diagram showing various options for adding common axes to the articulated arms of FIG. 1 for different procedures;

[0013]FIG. 7 is a schematic block diagram of the servo motors associated with the axis of FIGS. 1 and 6 and a controller for controlling the axes as well as the x-ray detector and x-ray source according to the present invention;

[0014]FIG. 8 is a functional diagram of tasks implemented by the controller of FIG. 7 to control the axes according to one embodiment of the invention;

[0015]FIG. 9 is a functional diagram task implemented by the controller of FIG. 7 to automatically or semi-automatically track a bolus according to one embodiment of invention;

[0016]FIG. 10 is a front elevational view of a supine patient showing the x-ray detector and x-ray source positioned by the present invention in the offset opposition; and

[0017]FIG. 11 is a perspective view of the x-ray detector and x-ray source of FIG. 10 showing offset collimation of the x-ray source and a region of interest display shown on the display x-ray detector assembly.

DETAILED DESCRIPTION

[0018] Referring now to FIG. 1, a multi-mode x-ray positioner 10 per the present invention provides an x-ray source 12 and an x-ray detector 14. The x-ray source 12 generally includes an x-ray tube, the necessary cooling components, collimators, and shielding as will be understood to those of ordinary skill in the art. The x-ray detector 14 may be a lightweight flat panel detector such as may be fabricated as an array of detectors, an amorphous silicon detector panel or other imaging device. The x-ray detector is part of a detector assembly 16 to be described in greater detail below.

[0019] The x-ray source 12 directs an x-ray beam generally along a central ray 13 whereas the x-ray detector 14 receives x-rays generally along a central ray 15 normal to the surface thereof. A patient 50 may be supported supine on a table 56 so as to be aligned with the central rays 13 and 15. For this purpose, the table 56 is composed of a radiotranslucent material of a type well known in the art.

[0020] Referring also to FIG. 4, each of the x-ray source 12 and the x-ray detector 14 are held, respectively, on separate articulated robot arms 18 and 20. The arms 18 and 20 are attached at a first end to a base 22, the latter preferably supported against a vertical surface with the arms extending laterally therefrom.

[0021] The arms 18 and 20 attach to the base 22 at shoulder axes 26 and 24, respectively. Each shoulder axes 26 and 24 provides angulation of its respective arm 18 or 20 about parallel axes extending generally along the plane of the base 22, the latter being parallel to a vertical plane defining the surface to which the base 22 is attached. Generally the term “axis” henceforth will refer both to a mechanical joint and the mathematical vector describing movement of that joint. The particular meaning will be evident from context.

[0022] Attached to and extending from shoulder axes 24 and 26 are upper arms 30 and 32, respectively, which terminate in elbow axes 34 and 36, respectively, each also providing for angulation along parallel axes also parallel to axes 24 and 26. Forearms 38 and 40 extend from elbow axes 34 and 36, respectively, and the latter which provide telescoping extension axes 42 and 44 permitting translation movement of wrist axes 46 and 48 along the length of the forearms 38 and 40.

[0023] Wrist axes 46 and 48 provide angulation about parallel axes also parallel to axes 24 and 26 and connect, respectively, to the x-ray detector assembly 16 and x-ray source 12. It is to be understood that the x-ray source and x-ray detector assembly are not limited to mounting on a particular arm and may be replaced by other devices to meet other clinical needs.

[0024] It will be understood from this description that each of the arms has four axes of motion comprised of shoulder axes 24, elbow axis 34 and wrist axis 46 and extension axis 42, for arm 20 and shoulder axes 26, elbow axis 36, and wrist axis 48, and extension axis 44 for arm 18. Generally, motion of shoulder axes 24 and 26 control the angle of upper arms 30 and 32 and the position of elbow axes 34 and 36 with respect to shoulder axes 24 and 26. Likewise, motion of elbow axes 34 and 36 control the angle of forearms 38 and 40 and the position of wrist axes 46 and 48 with respect to the elbow axes 34 and 36. Motion of extension axes 42 and 44 control the separation of elbow axis 34 and wrist axis 46 and elbow axis 36 and wrist axis 48, respectively, and motion of wrist axes 46 and 48 control the angle of detector 14 and x-ray source 12.

[0025] Each of axes 24, 26, 34, 36, 42, 44, 46, and 48 are enabled for servo control meaning that they may be moved electronically in response to a position and/or motion signal received from the axis so that precise positioning and/or velocity control of each axis may be had through a central controller or group of interconnected controllers as will be described below. The flexibility of arms 18 and 20 is particularly useful when tracking a contrast bolus propagation through blood vessels during, for example, x-ray peripheral angiography studies. In particular, a bolus of contrast medium is injected into a patient for the purposes of, for example, detecting an arterial blockage. Advantageously, the arms 18 and 20 may automatically position the source 12 and detector 14 to track the bolus as it flows through a patient's blood vessel. Furthermore, the source 12 and detector 14 may be positioned to optimize the viewing angle of the attending operator, as will be described in more detail below.

[0026] Referring again to FIGS. 1 and 4, the arms 18 and 20 may be maneuvered to position the x-ray source 12 and detector assembly 16 in alignment on opposite sides of a patient 50 at a first source-to-detector distance 52. Subsequently, the arms 20 may be maneuvered, through a combined motion of their axes, to provide a source-to-detector distance 54 substantially greater than source-to-detector distance 52, while maintaining alignment. Such separation is accomplished principally by a combined angulation and extension of the axes 24, 26, 34, 36, 42, 44, 46, and 48 and notably does not require an axis of translation aligned with the central rays 13 and 15 of the source and detector as is typical of conventional x-ray positioners.

[0027] Referring again to FIGS. 1 and 4, the base 22 may be mounted on a waist axis 64 providing rotation about a line that is horizontal and perpendicular 60 to the plane of the base 22, the rotation as indicated by arrow 62. Thus, the arms 18 and 20 in their various source-to-detector separations 52 and 54 shown in FIG. 4 may be opposed about a substantially vertical axis (as depicted in FIG. 1) or about a horizontal axis. The horizontal axis is useful for procedures such as chest x-rays or other situations where the patient is best imaged while standing or seated. In these cases, the table 56 would be moved to a vertical configuration or moved out of the way altogether. The rotation of the base 22 about the waist axis 64, as with the other axes, is under servo control and provides single axis cranial-caudal angular adjustment.

[0028] Alternatively as shown in FIG. 5, the arms 18 and 20 may be manipulated to provide central rays 13 and 15 perpendicular to the plane of the base 22. In this case, the arms 18 and 20 are not deployed symmetrically but elbow axis 34 is moved to an acute position whereas elbow axis 36 is moved to an obtuse position with extension axis 44 fully extended and extension axis 42 fully retracted. This degree of flexibility is accomplished because each of the axes 24, 26, 34, 36, 44, 42, 46 and 48 are independently controllable.

[0029] Referring to FIG. 6, the base 22 may be mounted directly on a wall or the like by means of stationary collar 70 receiving the waist axis 64. Alternatively, and as also shown in FIG. 6, the base 22 may be attached to a vertically translating collar 72 also receiving the waist axis 64 but providing for vertical translation along tracks 74 also under servo control to form translation axis 81. Opposed ends 76 of the track 74 may be held against the wall or vertical surface by stationary collars 78 (only one of which is shown for clarity) similar to stationary collar 70. The translation axis 81 allows single axis elevation of the x-ray source 12 and x-ray detector 16.

[0030] Alternatively, the end 76 may be received by horizontally translating collars 80 moving horizontally along tracks 82 so as to provide a horizontal servo control translation axis 85 for the tracks 74, the base 22, and thus the arms 18 and 20.

[0031] In an alternative configuration, the base 22 may be mounted to horizontally translating collar 90 of the tracks 92 positioned to extend horizontally along axis 91. The ends 94 of the tracks 92 may be attached either to a stationary collar 96, similar to stationary collars 78 or to horizontally vertically collars 98 but with the track 100 positioned to move along vertical axis 83, the latter having its ends 102 fixed to a stationary surface such as a wall or the like. The translation axis 91 allows single axis horizontal repositioning of the x-ray source 12 and x-ray detector 16.

[0032] While the two configurations represented in tree fashion by the branches ending with the axis 85 and 83 of FIG. 6 result in the same degrees of freedom, they provide alternate evolution paths allowing the positioner 10 to be upgraded from a base system having only base 22 and arms 18 and 20 to a full featured system through the addition, respectively, of various components of vertically translating collar 72, or horizontally translating collars 90. A wiring harness system (not shown) allows each of these axes to be added to an axis controller to provide improved functionality as will be described below.

[0033] Referring now to FIGS. 1, 2 and 3, the detector assembly 16 includes a flat panel x-ray detector 14 on a first surface normally facing the x-ray source 12 and held within a supporting frame 106. The flat panel x-ray detector 14 is sized to receive a collimated beam of x-rays 104 from the x-ray source 12 and positioned immediately behind the flat panel x-ray detector 14 is a blocking lead shield 110. This may be followed by processing circuit cards 112 and 114. Following the circuit cards 112 and 114 is a flat panel display 116.

[0034] The flat panel display 116 may receive an image registered with the image received by the x-ray detector 14 for display to a human operator viewing the image from the top side of the detector assembly 16. In this configuration, the image displayed by the flat panel display 116 remains in perfect registration with the x-ray detector 14 thus eliminating confusion that can result in normal fluoroscopy systems where the image may rotate on a stationary monitor with respect to the patient as the positioner is moved. As shown in FIG. 2, in order to provide for oblique viewing angles, the flat panel display 116 may hinge upward about one of two perpendicular hinge axes 128 or 130 so as to provide better viewing for the user while still maintaining rotational registration with the patient's anatomy.

[0035] Also supported on the top side of the frame 106 is a touch screen panel 118 providing for basic level control of the x-ray system including x-ray tube voltage, exposure time, and other techniques. The front portion of the frame 106 also supports a multi-axis control handle 120 providing a number of signals depending on movement of the handle by the operator either vertically, horizontally or in rotation as shown by arrows 124 and shown also in FIG. 2. A second blocking lead shield 108 may be attached to a portion of the supporting frame 106 positioned toward the operator during normal use as shown in FIG. 1.

[0036] The circuit cards 112 collect data from the x-ray detector 14 for a control system to be described. The circuit card 114 provides an interface for the control system with the touch screen panel 118 and a multi-axis control handle 120.

[0037] Referring now to FIG. 7, each of the different axes 24, 26, 34, 36, 42, 44, 46, 48, 64, 81, and 84 provides feedback signals and receives a command signals from an axis control interface 132 so as to provide for servo control of each axis according to techniques well known in the art. The axis control interface 132 connects to a central bus 134 of a controller 136. The controller 136 is constructed according to conventional computer architecture and includes a processor 138 communicating with the bus 134 and with memory 140 which may include both random access and magnetic disk memory or other mass storage devices. A modem 142 and/or device such as a network interface card also communicating with the bus provide pathways for downloading of information and programs into the memory 140 as will be described. The controller 136 may be a single computer or a number of interconnected computers providing the various functions and services.

[0038] The controller 136 also provides a signal through port interface 144 (also attached to bus 134) to a high voltage power supply 146 feeding the x-ray source 12 so as to provide control over current and x-ray tube voltage and on and off duty cycle. Diagnostic signals may also be received from the power supply 146 via this port interface. Additional ports interfaces 150, 152, and 154 provide communication between the central bus 134 and the control handle 120, the x-ray detector 14, the flat panel display 116, and the touch screen panel 118 described above.

[0039] During operation, the processor 138 runs a control program 170 held in memory 140 to control the various axes 24, 26, 34, 36, 42, 44, 46, 48, 64, 81, and 84 and to control the x-ray exposure of a patient and to receive and process the image data for display on the flat panel display 116 according to commands received through the control handle 120 and touch screen panel 118.

[0040] The memory 140 may also hold a hardware configuration file 160 and one or more personality files 162. The hardware configuration file 160 stores data on the various components as shown in FIG. 6 that have been assembled together to produce the particular positioner 10. The personality files 162 contain models for how the x-ray system will operate, for example, emulating a fluoroscopy system with a spot film device or C-arm type configuration. Each of the personality files 162 includes a zero configuration variable describing how the positioner 10 should be initialized prior to patient scan. More generally, the personality files 162 may include one or more predefined procedures involving dynamic movement of the arms 18 and 20 for a particular procedure such as tomography. The personality files 162 also define how the control handle 120 will be interpreted to axes movement.

[0041] For example, it may be desired to operate the positioner to emulate a fluoroscopy machine with a C-arm type structure. In this case, fluoroscopy C-arm type personality files 162 would be loaded and invoked through touch screen panel 118.

[0042] Referring now to FIG. 8, the control program 170 makes use of the configuration file 160 and the personality files 162 to implement control function blocks for the operation of the positioner 10. A first function block provides a control map 172 mapping movements of the control handle 120 to movements in a room coordinate system. For example, if the positioner 10 is programmed to emulate a C-arm type device, rotation of the control handle 120 may cause angulation of the C-arm effectively rotating the central rays 13 and 15 about a center point 174 shown in FIG. 7. The center point may be defined by the center of the base 22 or be arbitrarily located through multiple axis motion as determined by the personality file 162. Vertical and horizontal movement of the control handle 120 may raise or move laterally the virtual C-arm simultaneously moving the x-ray source 12 and x-ray detector 14 as if they were connected by a rigid bar. The assignment of the control handle 120 to particular room coordinates is arbitrary and even in this case, for example, they may be assigned differently with vertical movement of the control handle 120 changing source-to-detector distance rather than raising or lowering the x-ray detector 14 and x-ray source 12 in unison. Likewise, the motion of the positioner components with respect to each other may be arbitrarily defined to simulate positioners of varying geometries.

[0043] The control map 172 produces commands 178 in room coordinates or virtual machine coordinates (the latter which describe motion of machine components, such as a C-arm which do not in fact exist). The commands 178 are received by axis parsing and translation module 180 which interrogates the hardware configuration file 160 to see what axes are available in order to realize the coordinate commands 178. Generally there will be more than one combination of different axes movements and the axis parsing and translation module 180 will select among these looking at other considerations, for example, accessibility and the avoidance of collision within the patient space.

[0044] The axis parsing and translation module 180 translates the commands 178 into positioner axes commands 182 which are provided to one of the arms, preferably 20. The second arm 18 will receive positioner axis coordinates 184 from a virtual axis link 186. The virtual axis link 186 receiving as inputs the positioner axes commands 182 from the axis parsing and translation module 180 and providing corresponding positioner axis commands 184 to achieve the desired virtual linkage between the x-ray source 12 and x-ray detector 14 as defined by the configuration file 160 and the personality files 162. Generally this linkage will amount to simulation of a virtual structure directly connecting the x-ray source 12 and x-ray detector 14 together such as a bar or C-arm or the like.

[0045] Because the arms 18 and 20 are not so connected, a variety of other personalities may be adopted including those which provide for complex independent movement of the x-ray source 12 and x-ray detector 14 for tomography and the like.

[0046] As mentioned, a zero configuration variable may be read by the control program 170 to determine the starting position of the positioner 10, e.g., whether the x-ray source 12 and x-ray detector 14 are positioned horizontally with respect to each or laterally or for a standing patient or the like. Zero configuration task 190 handles this initialization of the axes making use of the hardware configuration file 160 and the particular machine model in personality files 162. The program 170 may also implement a procedure engine 192 which records particular procedures including techniques, exposure times, motion and positioning of the arms that may be collected and exchanged by physicians or skilled practitioners. These procedures may be invoked through the touch screen panel 118.

[0047] Referring to FIG. 7, the hardware configuration file 160 and the various personality files 162 may be loaded via the modem 142 and thus the positioner 10 may be configured remotely and users of the positioner 10 may trade different configurations, personality modules and procedures with each other as they are developed.

[0048] Referring now to FIG. 9, one such procedure may receive image data from the x-ray detector 14 into a summing unit 193 implemented by the program 170 and also into an image buffer 194. A subtraction of a previously buffered image and the current image yields motion data 195 which may be operated on by a morphometric filter 196 to identify, for example, a moving bolus of contrast medium in certain types of studies. The morphometric filter may be initialized by user parameters 202 that may be part of a procedure engine module being one of personality files 162.

[0049] The location of the bolus relative to the position of the x-ray detector 14 may be extracted as position coordinates 200 in the room or machine frame of reference. The position coordinates 200 may be fed directly to the control map 172 so as to provide for automatic bolus tracking in which the arms 18 and 20 are automatically moved so as to maintain a bolus of contrast medium within the x-ray beam. Memory 140 may also store images including video sequences and the like, user parameter data and other data well known in the art.

[0050] Referring to FIG. 1, the motion of the source and receptor can be manually controlled using control handle 120. The motion, or path, and variation of speeds along the path of the source and receptor may be recorded by the control system, and then may be accurately duplicated automatically, in either forward or reverse, during a procedure or during a subsequent procedure. This motion programmability, or recording, and repeatable non-linear motion is of particular advantage in vascular “run-off” or “bolus chasing” studies, in other studies where features of interest may move outside the field of view, or in temporal studies of the same patient. For instance, the attending operator may manually track a bolus traveling through a patient while the positioner 10 records the motion. Accordingly, when the patient is to be examined using a bolus at some other time, the path of the bolus may be automatically followed using the pre-programmed path. Data regarding a plurality of temporally spaced bolus tracking procedures may then be compared for a given patient.

[0051] The ability to program the motion in any direction, including rotational directions, allows the reduction or elimination of patient motion and improved flexibility in patient positioning. As a result, patient safety is enhanced and clinical efficiency improved with faster positioning, fewer repeated exposures, fewer contrast injections and improved useability of information from previous studies.

[0052] In accordance with an alternate embodiment, the positioner 10 may rely on the contrast of image intensity to identify the bolus, and automatically track the bolus as it travels through the patient, while relying on the increased degrees of freedom provided by the present invention to make the necessary translations and rotations to follow the bolus. As described above, the path of the bolus may be stored and referred to in subsequent bolus chasing procedures.

[0053] It should be appreciated that the bolus path may change from one time to another for a given patient due to unanticipated events. If the deviation in bolus path between the current instance and the previously stored path is significant, the bolus image would tend to move outside the display. Advantageously, the present invention allows for a user to manually override the automatic positioning to ensure that the entire path of the bolus is tracked. For example, the operator could rotate the source and detector as necessary, or could reduce or increase the speed of the source and detector to prevent the image from traveling outside the display. Alternatively, the positioner 10 could automatically rely on the image of the bolus to make any adjustments necessary to compensate for changes in the bolus path from one time to the next.

[0054] With the ability to program the source and receptor in any non-linear path, customized or programmed collimation of the source field may be accomplished to accommodate the morphology of the patient or other clinical need, and this program associated with the program for motion of the source and receptor. This customized position-associated, auto-collimation to control source field size provides several distinct advantages including the ability to reduce or eliminate the amount of needed bolus filtration, a means to reduce the amount of radiation exposure to the patient, and improvement in image quality with the reduction of X-Ray scatter.

[0055] Further, this expanded capability provides the ability to perform image subtraction and image pasting over a large area, and in any direction, with reduced error. In particular, the positioner 10 is capable of performing both short-term and long-term image subtraction to produce several substantially isolated images of the bolus as it travels through the patient. For example, an initial image of the patient may be recorded prior to injecting the bolus. Therefore, when the bolus is subsequently injected, the initial image of the patient may be subtracted from sequential images of the bolus as it travels through the patient to produce an image of substantially only the bolus. This will enable the attending operator to determine the size and shape of the bolus at various locations within the patient.

[0056] Furthermore, real-time images may be subtracted from the previous image (or other previously-obtained images) to produce a subtraction that would more reliably eliminate extraneous objects, such as the patient's bones, organs, and the like. Such a subtraction will produce a subtraction of the previous bolus image from the current bolus image, thereby producing a visible leading edge of the current image and potentially a trailing edge of the previous image to determine the rate of bolus travel during the time interval between the previous and current image. Additionally, the subtraction could be thresholded to subtract only those images having an image intensity less than the intensity of the bolus to produce an image of the entire bolus, thus illustrating its size and shape.

[0057] Referring now to FIG. 10, the small profile of the detector assembly 16 allows for more flexible positioning with respect to patient 50 than would be obtained with a comparable apertured image intensifier 210 shown in dotted outline. This flexibility is further enhanced by the ability to offset the central ray 13 of the x-ray source 12 with respect to the axis 15 of the x-ray detector 14 by displacement of the x-ray source or by offset collimation of the x-ray beam. In either case, when a small beam of x-rays is required, that beam may be directed to a desired area of the x-ray detector 14 rather than to the center of the x-ray detector 14 and that area preferentially scanned. This capability allows improved positioning with respect to the patient 50 without obstruction by the unused areas of the detector assembly 16 for large apertured x-ray detectors 14 or 210 such as may be desirable in particular positioning situations.

[0058] Referring to FIG. 11, as mentioned, the displacement of the central ray 13 may be performed by angulation of the x-ray source 12 through additional axes (not shown) or by adjustment of a collimator 212 to collimate the x-ray beam to less than the area of the detector but also to offset the center of the beam toward a detector edge. Control of a collimator 212 to control the exit aperture of the x-ray beam is well known in the art, and is modified only to displace the central ray 13 of the beam. Positioning of the detector assembly 16 may be enhanced by the generation of an x-ray reception pattern 214 on the face of the flat panel display 116, showing the operator the active area of the x-ray detector 14 on the opposite side of the detector assembly 16 prior to exposure.

[0059] It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but that modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments also be included as come within the scope of the following claims. 

1. A bolus tracking x-ray positioner comprising: an x-ray source producing an x-ray beam directed along a source axis; an x-ray detector detecting x-rays received along a detector axis; a first and second articulated arm holding respectively the x-ray source and the x-ray detector in opposition about a patient volume for movement along a bolus path; an axis controller operating according to a stored program to: (i) receive image signals from the x-ray detector (ii) process the image signals to identify movement of a bolus of contrast medium within a patient; and (iii) send movement signals to the first and second articulated arms to move the x-ray source and x-ray detector to follow the bolus with movement of the bolus through the patient.
 2. The bolus tracking x-ray positioner as recited in claim 1, wherein the processing of the image signals includes: comparing sequential image signals to detect regions of change processing the regions of change with morphometic filters to identify the bolus; and determining change in position of the bolus.
 3. The bolus tracking x-ray positioner as recited in claim 1, wherein the sending of movement signals centers the bolus within a field of view defined by the x-ray source and detector.
 4. The bolus tracking x-ray positioner as recited in claim 1, wherein the controller further determines changes of velocity and path.
 5. The bolus tracking x-ray positioner as recited in claim 4, wherein the path is pre-programmed in the controller.
 6. The bolus tracking x-ray positioner as recited in claim 5, wherein the controller sends movement signals to the articulated arms to rotate the source such that the source axis extends substantially normal to the path.
 7. The bolus tracking x-ray positioner as recited in claim 5, wherein the controller sends movement signals to the articulated arms to translate the source along the path.
 8. The bolus tracking x-ray positioner as recited in claim 1, further comprising a display terminal supported by the second articulated arm and disposed behind the detector with respect to the direction of x-ray beam travel, the display terminal being configured to receive electrical signals from the controller and produce an output image of the bolus.
 9. The bolus tracking x-ray positioner as recited in claim 8, wherein the movement signals ensure that the output image of the bolus is visible on the display.
 10. The bolus tracking x-ray positioner as recited in claim 1, wherein the movement signals cause the arms to rotate
 11. The bolus tracking x-ray positioner as recited in claim 1, wherein the motion signals cause the arms to translate.
 12. The bolus tracking x-ray positioner as recited in claim 1, wherein the position signals cause the source and detector to angulate while following the bolus movement.
 13. The bolus tracking x-ray positioner as recited in claim 1, wherein the processing further comprises subtracting a current image from a previous image to produce an isolated image of at least a portion of the bolus.
 14. The bolus tracking x-ray positioner as recited in claim 1, wherein the movement signals are recorded in memory.
 15. The bolus tracking x-ray positioner as recited in claim 14, further comprising a manual override to adjust one of the position and speed of the articulated arms while following the bolus. 